The present invention relates to rotary regenerative heat exchange apparatus and, more particularly, to rotary regenerative heat exchange apparatus specifically adapted for use in transferring heat from a very high temperature gas, such as process gas in the temperature range of 1800.degree. F. to 2500.degree. F., to a much cooler gas, such as ambient air.
In a typical rotary regenerative heat exchanger, a mass of heat exchange material carried in a rotor is first positioned in a passageway of a heating fluid where it absorbs heat from the fluid flowing therethrough. Then, upon further rotation of the rotor about its axis, the heated heat absorbent material is positioned in a second fluid passageway where its heat is transferred to and absorbed by a fluid to be heated passing through the second fluid passageway. The rotor is surrounded by a housing having end openings therein to provide for the passage of the heating fluid and the fluid to be heated through the first and second fluid passages respectively. Sealing means are provided at the ends of the rotor and about the circumference of the rotor and in closely spaced relationship with adjacent housing structure to prevent, or at least minimize, intermingling of the heating fluid and the fluid to be heated.
Rotary regenerative heat exchangers of this type provide an efficient method for transferring heat between two gases, typically a hot flue gas or process gas and air, and their use is quite common in temperatures that lie within the working range of steel or various alloys that are commonly used to comprise the heat exchanger structure and the metallic heat absorbent plates. However, for temperatures that lie above the working range of metals, as may prevail in various process applications, or in appreciation of material costs, it has been necessary to utilize ceramic materials for the heat absorbent element mass, and in certain instances for the supporting heat exchanger structure itself. Rotary regenerative heat exchangers utilizing ceramic heat absorbent material for high temperature application, are well known in the art. For example, U.S. Pat. Nos. 3,101,778 and 3,209,058 show high temperature heat exchangers wherein the rotor is formed of a plurality of sector-shaped blocks of axially perforate ceramic material, and U.S. Pat. Nos. 4,316,500 and 4,331,198 wherein the rotor is formed of one or more perforate ceramic disc.
Although rotors utilizing metallic heat absorbent element are quite suitable at low and moderate temperatures, such metallic element is not suitable at high temperatures due to temperature limitations of the material itself and also because contaminants in the fluids passing through the heat exchanger are often corrosive to metal in the higher temperature range. Ceramic element on the other hand is quite suitable for high temperature application but is often very brittle and liable to breakage when subjected to thermal stress or mechanical shock. Additionally, the ceramic element can be quite expensive as it is also difficult to make in the desired shapes necessary to properly fill the rotor of the heat exchanger with such ceramic element.
Accordingly, it is an object of the present invention to provide a rotary regenerative heat exchanger for use in transferring heat from a very high temperature gas to a very cool gas wherein both metallic and ceramic heat absorbent element are utilized with each being utilized in the temperature range for which it is more suitable.